Fix NPE in ReferenceVariantsHelper

#KT-6500 Fixed

compiler/frontend/src/org/jetbrains/jet/lang/resolve/DescriptorResolver.java

@@ -786,7 +786,7 @@ public class DescriptorResolver {
 
     public static void checkUpperBoundType(
             JetTypeReference upperBound,
-            JetType upperBoundType,
+            @NotNull JetType upperBoundType,
             boolean isClassObjectConstraint,
             BindingTrace trace
     ) {

core/descriptors/src/org/jetbrains/jet/lang/types/TypeUtils.java

@@ -299,7 +299,7 @@ public class TypeUtils {
         }
     }
 
-    public static boolean canHaveSubtypes(JetTypeChecker typeChecker, JetType type) {
+    public static boolean canHaveSubtypes(JetTypeChecker typeChecker, @NotNull JetType type) {
         if (type.isMarkedNullable()) {
             return true;
         }

idea/ide-common/src/org/jetbrains/jet/plugin/codeInsight/ReferenceVariantsHelper.kt

@@ -173,7 +173,7 @@ public class ReferenceVariantsHelper(
 
     private fun getQualifierRuntimeType(receiver: JetExpression): JetType? {
         val type = context[BindingContext.EXPRESSION_TYPE, receiver]
-        if (TypeUtils.canHaveSubtypes(JetTypeChecker.DEFAULT, type)) {
+        if (type != null && TypeUtils.canHaveSubtypes(JetTypeChecker.DEFAULT, type)) {
             val evaluator = receiver.getContainingFile().getCopyableUserData(JetCodeFragment.RUNTIME_TYPE_EVALUATOR)
             return evaluator?.invoke(receiver)
         }